As a projector for projecting images on a screen there has been a single-chip DLP (Digital Light Processing) projector that includes an illuminating optical device emitting multiple colors of light in a time division fashion and a reflection type image display device such as DMD (Digital Mirror Device) reflecting each color of light from the illuminating optical device toward the screen.
The illuminating optical device of a single-chip DLP projector, in general, includes a white light source and a color wheel that time-divides light from the white light source into multiple colors of light. The color wheel includes a disc having a plurality of transmissive regions each allowing a different color of light that passes therethrough and a motor for turning the disc. As the disc is rotated by the motor, the point on the disc on which the light from the white light source is incident changes, so that the light enters each of the transmission regions in turns. As a result, the color of light passing through the color wheel changes in a time division fashion. Here, the disc is formed with three transmissive regions that each transmit light of red(R), green(G) and blue(B) (which will be referred to hereinbelow as RGB).
The multiple colors of light emitted a in time division fashion from the illuminating optical device are modulated by the reflection type image display device and projected on the screen by way of a projection optical system. Accordingly, different colors of light are projected successively on the screen. In this process, if the rotational rate of the color wheel is so high that humans cannot perceive change of views, the projected image will be perceived as a synthesized color image of the different colors of light.
In the above configuration, as a method for enhancing luminance of the projected image, increasing the number of light sources can enhance the brightness of light that the light source emits. However, increasing the number of light sources results in an increase in power consumption. In contrast to this, as a method of enhancing luminance of the projected image without increasing power consumption, there is a method of enhancing the usage efficiency of light emitted from the light source by raising the ratio of the light that is transmitted through the color wheel to be incident on the DMD, to the light emitted from the light source.
Specifically, as a technology for raising usage efficiency of light, for example there is a means that can decrease the ratio of light blocked by the color wheel to the incident light, by providing additional transmissive regions that permit colors of light (e.g., white (W), yellow (Y), magenta (M), cyan (C) and the like) other than RGB, to pass therethrough.
Further, as another technological example for raising usage efficiency of light, Patent Document 1 discloses a projector which replaces the white light source with light sources that emit colors of light, instead of using additional transmissive regions for colors of light except for RGB. This projector includes a first light emitting diode that emits light containing red and green light; a second light emitting diode that emits blue light, a color wheel and a DMD.
In the projector disclosed in Patent Document 1, when, for example red light enters the DMD, light containing red and green light emitted from the first light emitting diode, is made incident on the red light transmissive region that transmits red light. In this case, only green light is blocked by the color wheel, but red light is permitted to pass. When white light from a white light source enters the red light transmissive region, light components other than green light are also blocked by the red light transmissive region. This is why the usage efficiency of light in the projector disclosed in Patent Document 1 can be raised compared to the case of using a white light source.
When colorful images such as movies etc., are projected, enhancement of color reproducibility is required. However, in order to enhance color reproducibility, it is necessary to limit the maximum brightness of each color light in order to adjust the balance between colors. As a result, luminance tends to be lowered. In this way, enhancement of the brightness of the projector and enhancement of color reproducibility stand in a trade-off relationship, hence it has been impossible to achieve high-luminance display and high-color reproducibility display at the same time.
For this reason, typical projectors have a plurality of display modes for dealing with various scenes in which the projector may be used such as a high-luminance mode for projecting a high-luminance image, a high color reproducibility mode for projecting a high-color reproducibility image. For example, when the projector is used for displaying presentation materials and the like, the high-luminance mode is used, whereas in a case of displaying the movie or the like, the high color reproducibility mode is used.